Read sensor with a uniform longitudinal bias stack

ABSTRACT

A read sensor with a uniform longitudinal bias (LB) stack is proposed. The read sensor is a giant magnetoresistance (GMR) sensor used in a current-in-plane (CIP) or a current-perpendicular-to-plane (CPP) mode, or a tunneling magnetoresistance (TMR) sensor used in the CPP mode. The transverse pinning layer of the read sensor is made of an antiferromagnetic Pt—Mn, Ir—Mn or Ir—Mn—Cr film. In one embodiment of this invention, the uniform LB stack comprises a longitudinal pinning layer, preferable made of an antiferromagnetic Ir—Mn—Cr or Ir—Mn film, in direct contact with and exchange-coupled to sense layers of the read sensor. In another embodiment of the present invention, the uniform LB stack comprises the Ir—Mn—Cr or Ir—Mn longitudinal pinning layer exchange coupled to a ferromagnetic longitudinal pinned layer, and a nonmagnetic antiparallel-coupling spacer layer sandwiched between and the ferromagnetic longitudinal pinned layer and the sense layers.

RELATED INVENTIONS

This is Application is a Divisional Application of U.S. patentapplication Ser. No. 11/065,225, entitled A READ SENSOR WITH UNIFORMLONGITUDINAL BIAS STACK, filed Feb. 23, 2005, which is incorporatedherein by reference as if fully set forth herein.

FIELD OF THE INVENTION

The present invention relates to a read sensor with ferromagnetic senselayers directly stabilized by a uniform longitudinal bias stack. Theread sensor is either a giant magnetoresistance (GMR) sensor used in acurrent-in-plane (CIP) or a current-perpendicular-to-plane (CPP) mode,or a tunneling magnetoresistance (TMR) sensor used in a CPP mode. Thelongitudinal bias stack mainly comprises an antiferromagnetic Ir—Mn—Crfilm.

BACKGROUND OF THE INVENTION

The heart of a computer is a magnetic disk drive. The magnetic diskdrive includes a rotating magnetic disk, a write/read head assembly thatis suspended by a suspension arm adjacent to a surface of the rotatingmagnetic disk, and an actuator that swings the suspension arm to placethe write/read head assembly over selected circular tracks on therotating magnetic disk. The write/read head assembly is directly locatedon a slider that has an air bearing surface (ABS) facing the surface ofthe magnetic disk. When the magnetic disk is stationary, the suspensionarm biases the slider into contact with the surface of the magneticdisk. When the magnetic disk rotates, air is swirled by the rotatingmagnetic disk. When the slider rides on the air bearing, the write/readassembly is employed for writing magnetic impressions to and readingmagnetic impressions from the rotating magnetic disk. The write/readhead assembly is connected to processing circuitry that operatesaccording to a computer program to implement the write and readfunctions.

The write/read head assembly includes a write head and a read head. Thewrite head includes first and second write-pole layers, a write-gaplayer, a coil layer, and first, second and third insulation layers (aninsulation stack). The write-gap layer, coil layer and insulation stackare sandwiched between the first and second write-pole layers. The firstand second write-pole layers are connected at the back of the writehead. Current conducted to the coil layer induces a magnetic flux in thefirst and second write-pole layers which cause a magnetic field tofringe out at the ABS of the write head for the purpose of writing theaforementioned magnetic impressions in circular data tracks on theaforementioned rotating magnetic disk.

Referring now to FIG. 1, there is shown a magnetic disk drive 100embodying this invention. As shown in FIG. 1, at least one rotatablemagnetic disk 112 is supported on a spindle 114 and rotated by a diskdrive motor 118. The magnetic recording is conducted by writing andreading circular data tracks (not shown) on the rotating magnetic disk112.

At least one slider 113 is positioned near the magnetic disk 112, eachslider 113 supporting one or more write/read head assemblies 121. As themagnetic disk 112 rotates, the slider 113 moves radially in and out overthe disk surface 122 so that the write/read head assembly 121 may accessdifferent circular data tracks on the disk surface 122. Each slider 113is attached to an actuator arm 119 with a suspension 115. The suspension115 provides a slight spring force which biases the slider 113 againstthe disk surface 122. Each actuator arm 119 is connected with a voicecoil motor (VCM) 127. The VCM 127 comprises a coil movable within afixed magnetic field, the direction and speed of the coil movementsbeing controlled by the motor current signals supplied by a control unit129.

During operation of the magnetic disk drive 100, the rotation of themagnetic disk 112 generates an air bearing between the slider 113 andthe disk surface 122, which exerts an upward force or lift on the slider113. The air bearing thus counter-balances the slight spring force ofthe suspension 115 and supports the slider 113 off and slightly abovethe disk surface 122 by a small, substantially constant spacing duringnormal operation.

The various components of the magnetic disk drive 100 are controlled inoperation by control signals generated by the control unit 129, such asaccess control signals and internal clock signals. Typically, thecontrol unit 129 comprises logic control circuits, storage means and amicroprocessor. The control unit 129 generates control signals tocontrol various system operations such as drive motor control signals online 123, and head position and seek control signals on line 128. Thecontrol signals on line 128 provide the desired current profiles tooptimally move and position the slider 113 to the desired circular datatrack on the disk surface 122. Write and read signals are communicatedto and from the write/read head assembly 121 with a recording channel125.

With reference to FIG. 2, the orientation of the write/read headassembly 121 in the slider 113 can be seen in more detail. FIG. 2 is anABS view of the slider 113, and as can be seen, the write/read headassembly 121, including a write head and a read head, is located at atrailing edge of the slider 113. The above description of a typicalmagnetic disk drive 100, and the accompanying illustration of FIGS. 1and 2 are for representation purposes only. It should be apparent thatthis invention may be embodied in other data storage systems similar tothe magnetic disk drive 100. These data storage systems may contain alarge number of magnetic disks and actuators, and each actuator maysupport a number of sliders.

A read head commonly used in a current-in-plane (CIP) mode, as shown inFIG. 3, includes first and second magnetic-shield layers (not shown),first and second read-gap layers 326, 328, a giant magnetoresistance(GMR) sensor 302 in a read region, longitudinal bias layers 330 in twoside regions, and conductor layers 332 also in the two side regions. TheGMR sensor 302, the longitudinal bias layers 330, and the conductorlayers 332 are sandwiched between the first and second read-gap layers326, 328, which are in turn sandwiched between the first and secondmagnetic-shield layers (not shown). A commonly used GMR sensor 302comprises Al—O/Ni—Cr—Fe/Ni—Fe seed layers 322, an antiferromagneticPt—Mn transverse pinning layer 316, a synthetic pinned-layer structure306 (comprising a ferromagnetic Co—Fe first pinned layer 310 with amagnetization 318, a nonmagnetic Ru spacer layer 314, and aferromagnetic Co—Fe second pinned layer 312 with a magnetization 320), anonmagnetic conducting Cu—O spacer layer 308, ferromagnetic Co—Fe/Ni—Fesense layers 304 with a magnetization 336, and a nonmagnetic Ta caplayer 324. In a quiescent position when a sense current is conductedthrough the GMR sensor 302, the magnetization 318 of the Co—Fe firstpinned layer 310 is rigidly pinned in a transverse directionperpendicular to and away from the ABS, the magnetization 320 of theCo—Fe second pinned layer 312 is also rigidly pinned in a directionperpendicular to but toward the ABS, and the magnetization 336 of theCo—Fe/Ni—Fe sense layers 304 is oriented in a longitudinal directionparallel to the ABS. During sensor operation, only the magnetization 336of the Co—Fe/Ni—Fe sense layers 304 is free to rotate in positive andnegative directions from the quiescent position in response to positiveand negative magnetic signal fields from the adjacent rotating magneticdisk.

The thickness of the Cu—O spacer layer 308 is chosen to be less than themean free path of conduction electrons through the GMR sensor 302. Withthis arrangement, a portion of the conduction electrons is scattered bythe interfaces of the Cu—O spacer layer 308 with the Co—Fe second pinnedlayer 312 and with the Co—Fe/Ni—Fe sense layers 304. When themagnetization 320 of the Co—Fe second pinned layer 312 and themagnetization 336 of the Co—Fe/Ni—Fe sense layers 304 are parallel toeach other, scattering is minimal. When the magnetizations 320, 336 areantiparallel to each other, scattering is maximal. Changes in scatteringalter the resistance of the GMR sensor 302 in proportion to cos θ, whereθ is the angle between the magnetizations 320, 336. During sensoroperation, the resistance of the GMR sensor 302 changes proportionallyto the magnitudes of the magnetic fields from the rotating magneticdisk, and these resistance changes cause potential changes that aredetected and processed as playback signals.

In the prior-art fabrication process of the GMR sensor 302 abutted withthe longitudinal bias layers 330 and conductor layers 332 in the twoside regions, as shown in FIG. 3, the GMR sensor 302 comprisingAl—O(3)/Ni—Cr—Fe(3)/Ni—Fe(0.4)/Pt—Mn(15)/Co—Fe(1.6)/Ru(0.8)/Co—Fe(1.6)/Cu—O(1.8)/Co—Fe(1)/Ni—Fe(1.6)/Ta(4)films (thickness in nm) is deposited in a deposition field of 100 Oe ona 8.2 nm thick Al₂O₃ first read-gap layer 326. A transverse-field annealis applied in a field of 50,000 Oe for 5 hours at 265° C. in a directionperpendicular to the deposition field. A monolayer photoresist isapplied and patterned in a photolithographic tool to mask the GMR sensor302 in a read region. Ion milling is then applied to entirely remove theGMR sensor 302 and partially remove the Al₂O₃ first read-gap layer intwo exposed side regions, in order to form sharp contiguous junctions.Longitudinal bias and conductor layers 330, 332, comprisingCr(15)/Co—Pt—Cr(10)/Rh(45) films are then deposited into the two exposedside regions, preferably with ion-beam sputtering at a normal angle forabutting the GMR sensor 302. The monolayer photoresist is lifted offwith assistance of chemical mechanical polishing (CMP). After asubsequent similar patterning process, recessed conductor layerscomprising Ta(10)/Cu(60)/Ta(10) films (not shown) are deposited. After amonolayer photoresist is lifted off, a 8.2 nm thick Al₂O₃ secondread-gap layer 328 is then deposited.

The GMR sensor 302 requires the transverse-field anneal to developstrong antiferromagnetic/ferromagnetic coupling between the Pt—Mntransverse pinning layer 316 and Co—Fe first pinned layer 310. Theanneal field must exceed the saturation field (H_(S)) of antiparallel(AP) ferromagnetic/ferromagnetic coupling across the Ru spacer layer 314(˜8,000 Oe) for aligning the magnetization 318 of the Co—Fe first pinnedlayer 310 and the magnetization 320 of the Co—Fe second pinned layer 312in the transverse direction. After cooling to room temperature, themagnetization 318 is rigidly pinned by the Pt—Mn transverse pinninglayer 316 in the transverse direction, while the magnetization 320 isrotated by 180°. A transverse flux closure will be formed between themagnetizations 318 and 320 after patterning, resulting in a small netmagnetization in the Co—Fe/Ru/Co—Fe synthetic pinned-layer structure306. This small net magnetization induces a small demagnetizing field(H_(D)) in the Co—Fe/Ni—Fe sense layers 304.

In this GMR sensor 302, antiferromagnetic/ferromagnetic coupling occursbetween the Pt—Mn transverse pinning layer 316 and the Co—Fe/Ru/Co—Fepinned-layer structure 306, producing a pinning field (H_(P)). ThisH_(P) must be high enough to rigidly pin the magnetizations 318 and 320of the Co—Fe/Ru/Co—Fe pinned layer structure 306 for proper sensoroperation. Ferromagnetic/ferromagnetic coupling also occurs across theCu—O spacer layer 308, producing a negative ferromagnetic coupling field(H_(F)). This H_(F) must be precisely controlled so that the sum ofH_(F) and H_(D) counterbalances a current-induced field (H_(I)) in theCo—Fe/Ni—Fe sense layers 304 (H_(F)+H_(D)=H_(I)), thereby orienting themagnetization 336 of the Co—Fe/Ni—Fe sense layers 304 in a longitudinaldirection parallel to the ABS for optimally biased sensor operation. Ina quiescent position, this GMR sensor 302 exhibits a resistance ofR_(o)+R_(A)+(½)R_(G), where R_(o) is a nonmagnetic resistance, R_(A) isthe maximum anisotropy magnetoresistance (AMR) of the Co—Fe/Ni—Fe senselayers 304, and R_(G) is the maximum giant magnetoresistance (GMR)resistance. When receiving a signal field from a rotating magnetic disk,the magnetization 336 rotates from the longitudinal direction, while themagnetizations 318, 320 remain unchanged. The rotation of themagnetization 336 changes the resistance of the GMR sensor 302 by±ΔR_(G) sin θ₁−ΔR_(A) sin² θ₁, where θ₁ is a rotation angle.

There are several disadvantages in the use of the GMR sensor with thishard magnetic stabilization scheme, as described in the prior art.First, to attain stable GMR responses, the Cr film in the side regionsmust be deposited thick enough to align die midplane of the Co—Pt—Crhard magnetic layer with that of the Co—Fe/Ni—Fe sense layers of the GMRsensor, and thus the Cr film at the contiguous junctions is inevitablythick. As a result, the separation between the sense layers and theCo—Pt—Cr hard magnetic layer becomes large, and the stabilizationefficiency is substantially reduced. Second, the Rh conductor layer mustbe thick enough to provide a low-resistance path, and thus substantialoverhangs at sides of the monolayer photoresist are formed. As a result,the liftoff process becomes difficult, and the sensor width cannot beprecisely determined. Third, the CMP is typically applied to facilitatethe liftoff process, and thus possible damages to the Co—Fe/Ni—Fe senselayers remain a concern. Fourth, in this hard magnetic stabilizationscheme, longitudinal bias fields provided by the Co—Pt—Cr hard magneticlayer are very non-uniform, which are high at edges of the sense layers,causing difficulties in rotating the magnetization of the sense layers,and are low at the center of the sense layers, causing difficulties instabilizing, the sense layers.

On the other hand, a read head 400 recently used in acurrent-perpendicular-to-plane (CPP) mode, as shown in FIG. 4, includesfirst and second magnetic-shield layers 426, 428, a tunnelingmagnetoresistance (TMR) sensor 402 (or a GMR sensor 402), a longitudinalbias (LB) stack 440, and insulating layers 430. The TMR sensor 402 isconnected with the first magnetic-shield layer 426 and overlaid with theLB stack 440, which is connected with the second magnetic-shield layer428.

The TMR sensor 402 comprises a Ta seed layer 422, an antiferromagneticPt—Mn transverse pinning layer 416, a synthetic pinned layer structure406 (comprising a ferromagnetic Co—Fe first pinned layer 410 having amagnetization 418, a nonmagnetic Ru spacer layer 414, and aferromagnetic Co—Fe second pinned layer 412 having a magnetization 420),a nonmagnetic insulating Al—O barrier layer 408, ferromagneticCo—Fe/Ni—Fe sense layers 404 having a magnetization 436, and anonmagnetic Cu cap layer 424. A recently used LB stack 440 comprises anonmagnetic Ru seed layer 442, a ferromagnetic Co—Fe longitudinal pinnedlayer 444 having a magnetization 438, an antiferromagnetic Ir—Mnlongitudinal pinning layer 446, and a nonmagnetic Ta cap layer 448.

In the prior-art fabrication process of a TMR sensor 402 overlaid withan LB stack 440 in a read region and abutted with insulating layers intwo side regions, as shown in FIG. 4, the TMR sensor 402 comprisingTa(6)/Pt—Mn(15)/Co—Fe(1.6)/Ru(0.8)/Co—Fe(1.8)/Al—O(0.8)/Co—Fe(1)/Ni—Fe(1.6)/Cu(2)films is deposited in a deposition field of 100 Oe on a 1 μm thick Ni—Fefirst magnetic-shield layer 426. The LB stack 440 comprisingRu(1)/Co—Fe(2.8)/Ir—Mn(7.5)/Ta(10) films is then subsequently depositedin the same deposition field on the TMR sensor. A transverse-fieldanneal is applied in a field of 50,000 Oe for 5 hours at 265° C. in adirection perpendicular to the deposition field. A longitudinal-fieldanneal is then applied in a field of 200 Oe for 2 hours at 240° C. in adirectional antiparallel to the deposition field. A monolayerphotoresist is applied and patterned in a photolithographic tool to maskthe TMR sensor 402 and the LB stack 440 in a read region. Ion milling isthen applied to entirely remove the LB stack 440 and the TMR sensor 402,and partially remove the Ni—Fe first magnetic-shield layer 426 in twoexposed side regions. A 50 nm thick Al₂O₃ insulating layer 430 is thendeposited into the two exposed side regions. The monolayer photoresistis lifted off, with assistance of CMP, and a 1 μm thick Ni—Fe secondmagnetic-shield layer 428 is then deposited.

The TMR sensor 402 requires the transverse-field anneal to developstrong antiferromagnetic/ferromagnetic coupling between the Pt—Mntransverse pinning layer 416 and the Co—Fe first pinned layer 410. Theanneal field must exceed the saturation field (H_(S)) of APferromagnetic/ferromagnetic coupling across the Ru spacer layer 414(˜8,000 Oe) for aligning the magnetization 418 of the Co—Fe first pinnedlayer 410 and the magnetization 420 of the Co—Fe second pinned layer412. After cooling to room temperature, the magnetization 418 is rigidlypinned by the Pt—Mn transverse pinning layer 416 in the transversedirection, while the magnetization 420 is rotated by 180°. A transverseflux closure will be formed between the magnetizations 418 and 420 afterpatterning, resulting in a small net magnetization in the Co—Fe/Ru/Co—Fesynthetic pinned-layer structure 406. This small net magnetizationinduces a small demagnetizing field (H_(D)) in the Co—Fe/Ni—Fe senselayers 404.

The LB stack 440 requires the longitudinal-field anneal to establishstrong ferromagnetic/anti ferromagnetic coupling between the Co—Felongitudinal pinned layer 444 and the Ir—Mn longitudinal pinning layer446. The anneal field only needs to exceed the unidirectional anisotropyfield (H_(UA)) of the as-deposited Co—Fe longitudinal pinned and Ir—Mnlongitudinal pinning layers 444, 446 (about 100 Oe) at 240° C. foraligning the magnetization 438 of the Co—Fe longitudinal pinned layer444 in a directional antiparallel to the deposition field. After coolingto room temperature, the magnetization 438 of the Co—Fe longitudinalpinned layer 444 is rigidly pinned by the Ir—Mn longitudinal pinninglayer 446. As a result, a longitudinal flux closure will be formedbetween the magnetization 438 of the Co—Fe longitudinal pinned layer 444and the magnetization 436 of the Co—Fe/Ni—Fe sense layers 404 afterpatterning, inducing magnetostatic interaction needed for stabilizingthe Co—Fe/Ni—Fe sense layers 404. Since this anneal field is much lowerthan the spin-flop field (H_(SF)) of AP coupling across the Ru spacerlayer 444 (˜1,000 Oe), the transverse flux closure between themagnetization 418 of the Co—Fe first pinned layer 410 and themagnetization 420 of the Co—Fe second pinned layer 412 is notinterrupted.

In this TMR sensor 402, antiferromagnetic/ferromagnetic coupling occursbetween the Pt—Mn transverse pinning layer 416 and the Co—Fe/Ru/Co—Fesynthetic pinned layer structure 406, producing a transverse pinningfield (H_(P)). This Hp must be high enough to rigidly pin themagnetizations 418 and 420 of the Co—Fe/Ru/Co—Fe synthetic pinned layerstructure 406 for proper sensor operation. Ferromagnetic/ferromagneticcoupling also occurs across the Al—O spacer layer, producing a positiveferromagnetic coupling field (H_(F)). This H_(F) must be preciselycontrolled to counterbalance H_(D) in the Co—Fe/Ni—Fe sense layers 404(H_(F)=H_(D)), thereby orienting the magnetization 436 of theCo—Fe/Ni—Fe sense layers 404 in a longitudinal direction parallel to theABS for optimally biased sensor operation. In a quiescent position, thisTMR sensor 402 exhibits a resistance of R_(o)+(½)ΔR_(T), where R_(o) isa nonmagnetic resistance, ΔR_(T) is the maximum tunnelingmagnetoresistance (TMR) resistance. When receiving a signal field from arotating magnetic disk, the magnetization 436 rotates from thelongitudinal direction, while the magnetizations 418, 420 and 438 remainunchanged. The rotation of the magnetization 436 changes the resistanceof the TMR sensor 402 by ±ΔR_(T) sin θ₁, where θ₁ is a rotation angle.

There are several disadvantages in the use of the TMR sensor with theantiferromagnetic stabilization scheme, as described in the prior art.First, the Pt—Mn transverse and Ir—Mn longitudinal pinning layersrequire the transverse-field and longitudinal-field anneals,respectively. While it is feasible to achieve the coexistence of thetransverse and longitudinal flux closures with this dual-annealapproach, it appears difficult in attaining a very high H_(UA) neededfor the longitudinal flux closure due to the inherent weakerantiferromagnetism in the Ir—Mn longitudinal pinning layer than thePt—Mn transverse pinning layer. Second, it is challenging to preciselycontrol the total thickness of nonmagnetic Cu and Ru films used asdecoupling layers. The Cu decoupling layer is needed to control themagnetostriction of the underlying sense layers, while the Ru decouplinglayer is needed to facilitate the LB stack to attain a high H_(UA).Their total thickness should be optimized in order to diminishferromagnetic/ferromagnetic coupling between the sense and longitudinalpinned layers, while still ensuring strong magnetostatic interactionsbetween the sense and longitudinal pinned layers. Third, in thisantiferromagnetic stabilization scheme, longitudinal bias fieldsprovided by the LB stack are very non-uniform, which are high at edgesof the sense layers, causing difficulties in rotating the magnetizationof the sense layers, and are low at the center of the sense layers,causing difficulties in stabilizing the sense layers.

In order to meet the ever increasing demand for improved data rate anddata capacity, researchers have found ways to make the read sensor eversmaller. For instance, by reducing the sensor width, researchers havebeen able to fit ever more tracks of data onto a given area of amagnetic disk. However, as the sensor widths decrease, the traditionalhard stabilization scheme for the GMR sensor used in the CIP mode, andthe antiferromagnetic stabilization scheme for either the GMR or TMRsensor used in the CPP mode, as described previously, becomeinsufficient to stabilize the sense layers. As discussed above, in thetraditional hard stabilization and antiferromagnetic stabilizationschemes, longitudinal bias layers magnetostatically couple to the outerside edges of the sense layers, providing strong longitudinal biasfields at edges of the read sensor. However, these longitudinal biasfields decay significantly toward the center of the read sensor. As theread sensor is made narrower, the demagnetizing field within the readsensor substantially increases, thus causing more difficulties instabilizing the sense layers. Hence, a novel stabilization scheme isneeded very much for the ever narrowed read sensor.

SUMMARY OF THE INVENTION

The present invention provides a read sensor, such as a giantmagnetoresistance (GMR) sensor used in a current-in-plane (CIP) or acurrent-perpendicular-to-plane (CPP) mode, or a tunnelingmagnetoresistance (TMR) sensor used in a CPP mode, with a uniformlongitudinal bias (LB) stack. The read sensor mainly includesferromagnetic sense layers, a synthetic pinned layer structure, and aspacer layer disposed therebetween. In the uniform LB stack of oneembodiment of this invention, an antiferromagnetic Ir—Mn—Cr pinninglayer is used to directly contact and exchange-couple to the senselayers. In the uniform LB stack of another embodiment of this theinvention, the antiferromagnetic Ir—Mn—Cr pinning layer is used tocontact and exchange-couple to a ferromagnetic Ni—Fe longitudinal pinnedlayer, and a nonmagnetic Ru spacer layer is sandwiched between theferromagnetic Ni—Fe longitudinal pinned layer and the ferromagneticsense layers for causing antiparallel exchange coupling across the Ruspacer layer. Both the read sensor and the uniform LB stack are locatedin a read region,

The read sensor and uniform LB stack may contact directly withconducting layers in two side regions. The Cr/Co—Pt—Cr longitudinal biaslayers used in the two side regions for the hard magnetic stabilizationscheme may be included in addition to the uniform LB stack, but arepreferably eliminated, since the uniform LB stack has been sufficient tostabilize the sense layers with a novel antiferromagnetic stabilizationscheme.

The present invention advantageously eliminates problems resulting fromcomplicated magnetics at edges of the read sensor, and the sensor widthcan be precisely controlled. The read sensor according to the presentinvention is thus advantageous for magnetic recording at ultrahighdensities.

The transverse pinning layer may be made of a Pt—Mn, Ir—Mn or Ir—Mn—Crfilm, while the longitudinal pinning layer may be made of either anIr—Mn or Ir—Mn—Cr film. Two anneals are applied in the fabricationprocesses of the read sensor, one for the formation of a transverse fluxclosure and the other for establishing longitudinal bias. A method ofoptimizing a longitudinal bias field needed for stabilizing the senselayers is proposed.

For each of the Pt—Mn, Ir—Mn and Ir—Mn—Cr transverse pinning layers,four types of read sensors may be used. The first and the second mayinclude a bottom-type read sensor, in which the transverse pinning layeris located below the sense layers. In the first type of read sensor, thesense layers are overlaid with an LB stack, which comprises the Ir—Mn orIr-M-Cr longitudinal pinning layer. In the second type of read sensor,the sense layers are overlaid with an LB stack, which comprises anonmagnetic Ru spacer layer, a ferromagnetic Ni—Fe or Co—Fe longitudinalpinned layer, and the Ir—Mn or Ir-M-Cr longitudinal pinning layer. Thethird and the fourth may include a top-type read sensor, in which thetransverse pinning layer is located above the sense layers. In the thirdtype of read sensor, the sense layers overlie an LB stack, whichcomprises the Ir—Mn or Ir-M-Cr longitudinal pinning layer. In the fourthtype of read sensor, the sense layers overlie an LB stack, whichcomprises the Ir—Mn or Ir-M-Cr longitudinal pinning layer, the Ni—Fe orCo—Fe longitudinal pinned layer, and the nonmagnetic Ru spacer layer.

The LB stack of this invention advantageously provides a uniformlongitudinal bias field for stabilizing the sense layers across theentire width of the read sensor. This and other features and advantagesof the invention will become apparent upon further reading of theDetailed Description in conjunction with the Figures.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the nature and advantages of thisinvention, as well as the preferred mode of use, reference should bemade to the following detailed description read in conjunction with theaccompanying drawings which are not to scale.

FIG. 1 is a schematic illustration of a magnetic disk drive in whichthis invention may be embodied;

FIG. 2 is an ABS view of a slider illustrating the location of a readsensor thereon;

FIG. 3 is an ABS view of a prior-art read head commonly used in acurrent-in-plane (CIP) mode, wherein a GMR sensor is included;

FIG. 4 is an ABS view of a prior-art read head recently used in acurrent-perpendicular-to-plane (CPP) mode, wherein a TMR sensor isincluded;

FIG. 5 is an ABS view of a read head according to an embodiment of thisinvention, wherein a bottom-type GMR sensor and a uniform LB stack areincluded;

FIG. 6 is an ABS view of another read head according to an alternateembodiment of this invention, wherein a bottom-type GMR sensor andanother uniform LB stack are included;

FIG. 7 is an ABS view of a yet another read head according to yetanother embodiment of this invention, wherein a top-type GMR sensor anda uniform LB stack are included;

FIG. 8 is an ABS view of a yet another read head according to yetanother embodiment of this invention, wherein a top-type GMR sensor andanother uniform LB stack are included;

FIG. 9 is a plot showing the easy-axis coercivity (H_(CE)) and theunidirectional anisotropy field (H_(UA)) versus the Ir—Mn—Cr filmthickness forAl—O(3)/Ni—Cr—Fe(3)/Ni—Fe(0.4)/Ir—Mn—Cr/Ni—Fe(2.4)/Co—Fe(1)/Cu—O(2.4)/Ta(4)films (thickness in nm);

FIG. 10 is a plot showing easy-axis and hard-axis hysteresis loops ofmagnetic moment (m) versus field (H) for a top-type GMR sensor,comprisingAl—O(3)/Ni—Cr—Fe(3)/Ni—Fe(1.6)/Co—Fe(1)/Cu—O(1.8)/Co—Fe(1.6)/Ru(0.8)/Co—Fe(1.6)/Ir—Mn—Cr(5)/Ta(4),and a top-type GMR sensor overlying a uniform LB stack, comprisingAl—O(3)/Ni—Cr—Fe(3)/Ni—Fe(0.4)/Ir—Mn—Cr(5)/Ni—Fe(2.4)/Co—Fe(1)/Cu—O(1.8)/Co—Fe(1.6)/Ru(0.8)/Co—Fe(1.6)/Ir—Mn—Cr(5)/Ta(4)films;

FIG. 11 is a plot showing the easy-axis loops of magnetoresistance (R)versus field (H) for a top-type GMR sensor, comprisingAl—O(3)/Ni—Cr—Fe(3)/Ni—Fe(1.6)/Co—Fe(1)/Cu—O(1.8)/Co—Fe(1.6)/Ru(0.8)/Co—Fe(1.6)/Ir—Mn—Cr(5)/Ta(4),and a top-type GMR sensor overlying a uniform LB stack, comprisingAl—O(3)/Ni—Cr—Fe(3)/Ni—Fe(0.4)/Ir—Mn—Cr(5)/Ni—Fe(2.4)/Co—Fe(1)/Cu—O(1.8)/Co—Fe(1.6)/Ru(0.8)/Co—Fe(1.6)/Ir—Mn—Cr(5)/Ta(4)films;

FIG. 12 is a plot showing H_(CE) and H_(UA) versus the Ir—Mn—Cr filmthickness forAl—O(3)/Ni—Cr—Fe(3)/Ni—Fe(0.4)/Ir—Mn—Cr/90Co-10Fe(2.4)/Cu(2.4)/Ta(4)films;

FIG. 13 is a plot showing H_(CE) and H_(UA) versus the Ir—Mn—Cr filmthickness forAl—O(3)/Ni—Cr—Fe(3)/Ni—Fe(0.4)/Ir—Mn—Cr/77Co-23Fe(2.4)/Cu(2.4)/Ta(4)films; and

FIG. 14 is a plot showing H_(CE) and H_(UA) versus the Cr content of theIr—Mn—Cr film forAl—O(3)/Ni—Cr—Fe(3)/Ni—Fe(0.4)/Ir—Mn—Cr(7.5)/Ni—Fe(4)/Cu(2.4)/Ta(4) andAl—O(3)/Ni—Cr—Fe(3)/Ni—Fe(0.4)/Ir—Mn—Cr(7.5)/70Co-30Fe(2.4)/Cu(2.4)/Ta(4)films.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description is of the best embodiments presentlycontemplated for carrying out this invention. This description is madefor the purpose of illustrating the general principles of this inventionand is not meant to limit the inventive concepts claimed herein.

The read head mainly includes a read sensor and a uniform LB stack,which are fabricated according to this invention. The read sensor can beeither a giant magnetoresistance (GMR) sensor used in either acurrent-in-plane (CIP) or current-perpendicular-to-plane (CPP) mode, ora tunneling magnetoresistance (TMR) sensor used in either the CPP mode.For purposes of illustration, only the GMR sensor used in the CIP modewill be described.

With reference now to FIG. 5, a read head 500 according to an embodimentof this invention includes first and second magnetic-shield layers (notshown), first and second read-gap layers 502, 504, a bottom-type GMRsensor 506, a uniform LB stack 508, and conductor layers 510. Thebottom-type GMR sensor 506, the uniform LB stack 508, and the conductorlayers 510 are sandwiched between the first and second read-gap layers502, 504, which are in turn sandwiched between the first and secondmagnetic-shield layers (not shown).

The bottom-type GMR sensor 506 includes Al—O/Ni—Cr—Fe/Ni—Fe seed layers512, an antiferromagnetic Ir—Mn—Cr (or Ir—Mn or Pt—Mn) transversepinning layer 514, a synthetic pinned-layer structure 516 (comprising aferromagnetic Co—Fe first pinned layer 518 with a magnetization 538, anonmagnetic Ru spacer layer 520, and a ferromagnetic Co—Fe second pinnedlayer 522 with a magnetization 540), a nonmagnetic conducting Cu—Ospacer layer 524, and ferromagnetic Co—Fe/Ni—Fe sense layers 526 with amagnetization 536. The uniform LB stack 508 comprises anantiferromagnetic Ir—Mn—Cr (or Ir—Mn) longitudinal pinning layer 528 anda nonmagnetic Ta cap layer 530.

The Ir—Mn—Cr transverse pinning layer 514 “rigidly pins” the netmagnetization of the synthetic pinned layer structure 516, therebyachieving proper sensor operation. On the other hand, the Ir—Mn—Crlongitudinal pinning layer 528 “optimally pins” the magnetization 536 ofthe Co—Fe/Ni—Fe sense layers 526, thereby not only overcoming strong thedemagnetizing field within the sense layers 526, but also longitudinallybiasing the sense layers 526. When receiving a signal field from arotating magnetic disk, the magnetization 536 of the sense layers 526 isstill free to rotate from the longitudinal direction, while themagnetizations 538, 540 of the synthetic pinned-layer structure 516remain unchanged. This rotation changes the resistance of the GMR sensor506 by +ΔR_(G) sin θ₁−ΔR_(A) sin²θ₁ where θ₁ is a rotation angle.

With reference to FIG. 6, a read head 600 according to an alternateembodiment of this invention includes first and second magnetic-shieldlayers (not shown), first and second read-gap layers 602, 604, abottom-type GMR sensor 606, a uniform LB stack 608, and conductor layers610. The bottom-type GMR sensor 606, the uniform LB stack 608, and theconductor layers 610 are sandwiched between the first and secondread-gap layers 602, 604, which are in turn sandwiched between the firstand second magnetic-shield layers (not shown).

The bottom-type GMR sensor 606 comprises Al—O/Ni—Cr—Fe/Ni—Fe seed layers612, an antiferromagnetic Ir—Mn—Cr (or Ir—Mn or Pt—Mn) transversepinning layer 614, a synthetic pinned-layer structure 616 (comprising aferromagnetic Co—Fe first pinned layer 618 having a magnetization 621, anonmagnetic Ru first spacer layer 620, and a ferromagnetic Co—Fe secondpinned layer 622 having a magnetization 623), a nonmagnetic conductingCu—O spacer layer 624, and ferromagnetic Co—Fe/Ni—Fe sense layers 626having a magnetization 636. The uniform LB stack 608 comprises anonmagnetic Ru second spacer layer 628, a ferromagnetic Ni—Fe (or Co—Fe)longitudinal pinned layer 630 having a magnetization 638, anantiferromagnetic Ir—Mn—Cr (or Ir—Mn) longitudinal pinning layer 632,and a nonmagnetic Ta cap layer 634.

The Ir—Mn—Cr transverse pinning layer 614 “rigidly pins” the netmagnetization of the synthetic pinned layer structure 616, therebyachieving proper sensor operation. On the other hand, the Ir—Mn—Crlongitudinal pinning layer 632 “optimally pins” the net magnetization ofthe Co—Fe/Ni—Fe sense layers 626 and the Ni—Fe longitudinal pinnedlayers 630, thereby not only overcoming strong the demagnetizing fieldwithin the sense layers 626, but also longitudinally biasing the senselayers 626.

With reference now to FIG. 7, a read head 700 according to yet anotherembodiment of this invention includes first and second magnetic-shieldlayers (not shown), first and second read-gap layers 702, 704, a uniformLB stack 706, a top-type GMR sensor 708, and conductor layers 710. Theuniform LB stack 706, the top-type GMR sensor 708, and the conductorlayers 710 are sandwiched between the first and second read-gap layers702, 704, which are in turn sandwiched between the first and secondmagnetic-shield layers (not shown).

The uniform LB stack 706 comprises Al—O/Ni—Cr—Fe/Ni—Fe seed layers 712and an antiferromagnetic Ir—Mn—Cr (or Ir—Mn) longitudinal pinning layer714. The top-type GMR sensor 708 comprises ferromagnetic Ni—Fe/Co—Fesense layers 716 having a magnetization 736, a nonmagnetic conductingCu—O spacer layer 718, a synthetic pinned-layers structure 720(comprising a ferromagnetic Co—Fe first pinned layer 722 having amagnetization 732, a nonmagnetic Ru spacer layer 724, and aferromagnetic Co—Fe second pinned layer 726 having a magnetization 734),an antiferromagnetic Ir—Mn—Cr (or Ir—Mn or Pt—Mn) transverse pinninglayer 728, and a nonmagnetic Ta cap layer 730.

With reference now to FIG. 8, a read head 800 according to still anotherembodiment of this invention includes first and second magnetic-shieldlayers (not shown), first and second read-gap layers 802, 804, a uniformLB stack 806, a top-type GMR sensor 808, and conductor layers 810. Theuniform LB stack 806, the top-type GMR sensor 808, and the conductorlayers 810 are sandwiched between the first and second read-gap layers802, 804, which are in turn sandwiched between the first and secondmagnetic-shield layers (not shown).

The uniform LB stack 806 comprises Al—O/Ni—Cr—Fe/Ni—Fe seed layers 812,an antiferromagnetic Ir—Mn—Cr (or Ir—Mn) longitudinal pinning layer 814,a ferromagnetic Ni—Fe (or Co—Fe) longitudinal pinned layer 816 having amagnetization 838, and a nonmagnetic Ru first spacer layer 818. Thetop-type GMR sensor 808 comprises ferromagnetic Ni—Fe/Co—Fe sense layers820 having a magnetization 836, a nonmagnetic conducting Cu—O spacerlayer 822, a synthetic pinned-layer stricture 824 (comprising aferromagnetic Co—Fe first pinned layer 826 having a magnetization 827, anonmagnetic second Ru spacer layer 828, and a ferromagnetic Co—Fe secondpinned layer 830 having a magnetization 831), an antiferromagneticIr—Mn—Cr (or Ir—Mn or Pt—Mn) transverse pinning layer 832, and anonmagnetic Ta cap layer 834.

The fabrication process of these four types of GMR sensors as shown inFIGS. 5, 6, 7 and 8, will be described below. The top-type GMR sensor700 as shown in FIG. 7 will be used for the description. The uniform LBstack 706 and the top-type GMR sensor 708 are sequentially deposited ina deposition field of about 100 Oe on a 5.5 nm thick Al₂O₃ firstread-gap layer 702. The longitudinal LB stack 706 compriseAl—O(3)/Ni—Cr—Fe(3)/Ni—Fe(0.4)/Ir—Mn—Cr(5) films (thickness in nm). Thetop-type GMR sensor 708 comprisesNi—Fe(2.4)/Co—Fe(1)/Cu—O(1.8)/Co—Fe(1.6)/Ru(0.8)/Co—Fe(1.6)/Ir—Mn—Cr(5)/Ta(4)films. A transverse-field anneal is applied in a field of 50,000 Oe for5 hours at 240° C. in a direction perpendicular to the deposition field.A longitudinal-field anneal is then applied in a field of about 200 Oefor 2 hours at 240° C. in a direction parallel to the deposition field.A monolayer photoresist is applied and patterned in a photolithographictool to mask the uniform LB stack 706 and the top-type GMR sensor 708 ina read region. Ion milling is then applied to entirely remove theuniform LB stack 706 and the top-type GMR sensor 708, and partiallyremove the Al₂O₃ first read-gap layer 702 in two exposed side regions.However, a partial ion milling process wherein the LB stack 706 is notentirely removed may also be employed. Conductor layers 710 comprisingCr(3)/Rh(75) films are then deposited into the two exposed side regions.The monolayer photoresist is lifted off, with assistance of CMP. In asubsequent similar patterning process, recessed conductor layers (notshown) comprising Ta(10)/Cu(60)/Ta(10) films are deposited. After amonolayer photoresist is lifted off, a 5.5 nm thick Al₂O₃ secondread-gap layer 704 is then deposited.

The top-type GMR sensor 700 requires the transverse-field anneal toestablish strong ferromagnetic/antiferromagnetic coupling between thesynthetic pinned-layer structure 720 and the Ir—Mn—Cr transverse pinninglayer 728. The anneal field must exceed the saturation field (H_(S)) ofantiparallel ferromagnetic/ferromagnetic coupling across the Ru secondspacer layer 724 (˜8,000 Oe) for aligning the magnetization 732 of theCo—Fe first pinned layer 722 and the magnetization 734 of the Co—Fesecond pinned layer 726 in the transverse direction. After cooling toroom temperature, the magnetization 734 of the Co—Fe second pinned layer726 is rigidly pinned by the Ir—Mn—Cr transverse pinning layer 728 inthe transverse direction, while the magnetization 732 of the Co—Fe firstpinned layer 722 is rotated by 180°. A transverse flux closure will beformed between the magnetizations 732, 734 after patterning, resultingin a small net magnetization in the Co—Fe/Ru/Co—Fe syntheticpinned-layer structure 720. This small magnetization induces a smalldemagnetizing field (H_(D)) in the Ni—Fe/Co—Fe sense layers 716.

The uniform LB stack 706 requires the longitudinal-field anneal toestablish medium antiferromagnetic/ferromagnetic coupling between theIr—Mn—Cr longitudinal pinning layer 714 and the sense layer 716. Theanneal field only needs to exceed the unidirectional anisotropy field(H_(UA)) at 240° C. of the Ir—Mn—Cr longitudinal pinning layer 714 andthe sense layer 716 (below 100 Oe) for aligning the magnetization 736 ofthe sense layer 716 in the longitudinal direction. After cooling to roomtemperature, the magnetization 736 of the sense layers 716 is “optimallypinned” by the Ir—Mn—Cr longitudinal pinning layer 714 in thelongitudinal direction. A uniform longitudinal bias field, equivalent tothe difference between the H_(UA) and the demagnetizing field, isproduced for the stabilization of the sense layers 716. Since thisanneal field is much lower than the spin-flop field (H_(SF)) ofantiparallel ferromagnetic/ferromagnetic coupling across the Ru spacerlayer 724 at 240° C. (1,000 Oe), the transverse flux closure between themagnetizations 732, 734 is not interrupted.

In this top-type GMR sensor 708 overlying the uniform LB stack 706,ferromagnetic/antiferromagnetic coupling occurs between theCo—Fe/Ru/Co—Fe synthetic pinned-layer structure 720 and the Ir—Mn—Crtransverse pinning layer 728, producing a transverse pinning field(H_(P)). This H_(P) must be high enough to rigidly pin the netmagnetization of the Co—Fe/Ru/Co—Fe synthetic pinned-layer structure 720in the transverse direction for proper sensor operation.Ferromagnetic/ferromagnetic coupling also occurs across the Cu—O spacerlayer 718, producing a negative ferromagnetic coupling field (H_(F)).This H_(F) must be precisely controlled so that the sum of H_(F) andH_(D) counterbalances a current-induced field (H_(I)) in the senselayers 716 (H_(F)+H_(D))=H_(I)), thereby orienting the magnetization 736of the sense layers 716 in the longitudinal direction for optimallybiased sensor operation. In a quiescent position, this GMR sensorexhibits a resistance of R_(o)+ΔR_(A)+(½)ΔR_(G), where R_(o) is anonmagnetic resistance, R_(A) is the maximum anisotropymagnetoresistance (AMR) of the sense layers 716, and R_(G) is themaximum giant magnetoresistance (GMR) resistance. When receiving asignal field from a rotating magnetic disk, the magnetization 736 of thesense layers 716 is still free to rotate from the longitudinaldirection, while the magnetizations 732, 734 of the synthetic pinnedlayer structure 720 remain unchanged. This rotation changes theresistance of the GMR sensor 708 by ±ΔR_(G) sin θ₁−ΔR_(A) sin²θ₁, whereθ₁ is a rotation angle.

To ensure the viability of this invention, it is necessary to attain anoptimal H_(UA) for stabilizing the sense layers 716. This H_(UA) must behigh enough to not only overcome the demagnetizing field within thesense layers 716, but also longitudinally bias the sense layers 716.This H_(UA) must also be low enough to minimize a loss in signalsensitivity. Modeling indicates that, the optimal H_(UA) substantiallyincreases when miniaturizing the top-type GMR sensor 708 for magneticrecording at ever increasing densities. For example, for a top-type GMRsensor with 40 nm in width and 40 nm in height, the sense layers 716with a magnetic moment of 0.24 memu/cm² (equivalent to that of a 3 nmthick Ni—Fe sense layer) require an H_(UA) of 250 Oe to stabilize thesense layers 716 while maintaining reasonably high signal sensitivity.This modeling result is quite unexpected since the required H_(UA) wasspeculated to range from 20 to 40 Oe for a prior-art large top-type GMRsensor having a low demagnetizing field with the sense layers. As thesensor height and width further decrease for magnetic recording at everincreasing densities, the needed H_(UA) is predicted to be as high as500 Oe. This optimal H_(UA) is attained by utilizing theAl—O/Ni—Cr—Fe/Ni—Fe seed and Ir—Mn—Cr pinning layers with optimalthicknesses and compositions, as described below.

FIG. 9 shows the easy-axis coercivity (H_(CE)) and the unidirectionalanisotropy field (H_(UA)) versus the Ir—Mn—Cr film thickness forAl—O(3)/Ni—Cr—Fe(3)/Ni—Fe(0.4)/Ir—Mn—Cr/Ni—Fe(2.4)/Co—Fe(1)/Cu—O(2.4)/Ta(4)films (thickness in nm). Without the Al—O, Ni—Cr—Fe and Ni—Fe seedlayers, H_(CE) is below 10 Oe while H_(UA) is nearly zero (not shown)over a wide Ir—Mn—Cr thickness range. With these three seed layershaving optimal thicknesses and compositions, the polycrystalline grainsof the Ir—Mn—Cr longitudinal pinning layer and the Ni—Fe/Co—Fe senselayers become substantially large, thus substantially increasing bothH_(CE) and H_(UA). The Ir—Mn—Cr longitudinal pinning layer must bethicker than 3 nm to attain a reasonably low H_(CE) and a high H_(UA).Its thickness is selected based on the modeling of a read sensor withdesigned geometries for determining a needed H_(UA). For example, a 5 nmthick Ir—Mn—Cr longitudinal pinning layer is selected for the uniform LBstack, in order to attain an H_(UA) of 250 Oe for a read sensor with 40nm in width and 40 nm in height. Since H_(UA) is inversely proportionalto the magnetic moment, a 5 nm thick Ir—Mn—Cr transverse pinning layercan also be selected for the read sensor, and the H_(UA) can be infiniteafter zeroing the net magnetic moment of the synthetic pinned-layerstructure. Hence, with the same Ir—Mn—Cr films used as the longitudinaland transverse pinning layers, the sense layers can be “optimally”pinned” while the synthetic pinned-layer structure can be “rigidlypinned”.

FIG. 10 shows easy-axis and hard-axis hysteresis loops of magneticmoment (m) versus field (H) for a top-type GMR sensor, comprisingAl—O(3)/Ni—Cr—Fe(3)/Ni—Fe(1.6)/Co—Fe(1)/Cu—O(1.8)/Co—Fe(1.6)/Ru(0.8)/Co—Fe(1.6)/Ir—Mn—Cr(5)/Ta(4),and for a top-type GMR sensor overlying an LB stack, comprisingAl—O(3)/Ni—Cr—Fe(3)/Ni—Fe(0.4)/Ir—Mn—Cr(5)/Ni—Fe(2.4)/Co—Fe(1)/Cu—O(1.8)/Co—Fe(1.6)/Ru(0.8)/Co—Fe(1.6)/Ir—Mn—Cr(5)/Ta(4)films. Without the uniform LB stack, die top-type GMR sensor shows goodsense-layer properties such as H_(C)=2.7 Oe and H_(F)=−16.4 Oe. With theuniform LB stack, the top-type GMR sensor shows sense-layers propertiessuch as H_(C)=29.3 Oe and H_(UA)=(259.4−16.4)=243.0 Oe. As predicted bymodeling, such a high H_(UA) is needed to not only overcome thedemagnetizing field in the sense layers, but also longitudinally biasthe sense layers. It should be noted that, in spite of the sense layer'shigh coercivity, the hard-axis hysteresis loop is nearly closed,indicating that transfer curve attained during sensor operation can benearly closed.

FIG. 11 shows the easy-axis loops of magnetoresistance (R) versus field(H) for a top-type GMR sensor, comprisingAl—O(3)/Ni—Cr—Fe(3)/Ni—Fe(1.6)/Co—Fe(1)/Cu—O(1.8)/Co—Fe(1.6)/Ru(0.8)/Co—Fe(1.6)/Ir—Mn—Cr(5)/Ta(4),and for a top-type GMR sensor overlying an LB stack, comprisingAl—O(3)/Ni—Cr—Fe(3)/Ni—Fe(0.4)/Ir—Mn—Cr(5)/Ni—Fe(2.4)/Co—Fe(1)/Cu—O(1.8)/Co—Fe(1.6)/Ru(0.8)/Co—Fe(1.6)/Ir—Mn—Cr(5)/Ta(4)films. Due to current shunting caused by the uniform LB stack, the GMRcoefficient of the top-type GMR sensor decreases from 14.8% to 11.5%.

As expected, the use of the uniform LB stack 706 for the top-type GMRsensor 708 causes degradation of sense-layer and GMR properties. Itshould be noted that, however, once the top-type GMR sensor 708overlying the uniform LB stack 706 is implemented into a sensorenvironment, several emerging advantages will compensate for thedisadvantages. First, without the use of decoupling layers between thelongitudinal pinning layer 714 and the sense layers 716, theunidirectional anisotropy field (H_(UA)) needed for the longitudinalbias can be much lower than that used in the prior art. As a result, itbecomes much easier to find a suitable antiferromagnetic film for theuse as the longitudinal pinning layer 714. Second, the longitudinal biasfield becomes uniform, instead of being very non-uniform in theprior-art hard-magnetic and antiferromagnetic stabilization schemes, sothat the sense layers 716 can be completely stabilized. Third, thesensor width can be precisely controlled since an uncertainty indefining the sensor width, due to complicated magnetics at sensor edgesbetween the read and side regions, is eliminated. Fourth, in spite oflower signal sensitivity, signal fields can be sensed effectively by theentire read sensor. In contrast, in the prior art, no signal fields canbe sensed from two sensor edges due to sense-layer stiffness at sensoredges, while signal fields with noises can be sensed from the center ofthe read sensor due to sense-layer instability in the center of the readsensor. Fifth, since only the conductor layers, instead of longitudinalbias and conductor layers used in the prior art, are deposited into thetwo exposed side regions, overhangs on the monolayer photoresist aremuch thinner and thus only a milder CMP is needed. As a result, therewill be less concerns on losses in signal amplitudes and on signalnoises due to mechanical and magnetic damages caused by the CMP.

To use the ever smaller read sensor for magnetic recording at everincreasing densities, the suppression of signal noises has beenconsidered more stringent than the increase in signal amplitudes. Anever increasing demagnetizing field in the read sensor must be overcomebefore stabilizing the sense layers. Hence, when the read-sensorminiaturization technology continues. the read sensor with the uniformLB stack according to this invention is expected to be more viable thanthe read sensor used in the prior art

Furthermore, modeling even indicates that, in order to reduce magneticnoises for a higher signal-to-noise ratio, the required H_(UA) for aread sensor with below 40 nm in width and below 40 nm in height need toexceed 1,000 Oe. To attain such an unexpected high H_(UA), aferromagnetic Co—Fe film need to be sandwiched between the Ir—Mn—Crlongitudinal pinning layer 714 and the Ni—Fe/Co—Fe sense layers 716.FIG. 12 shows H_(CE) and H_(UA) versus the Ir—Mn—Cr film thickness forAl—O(3)/Ni—Cr—Fe(3)/Ni—Fe(0.4)/Ir—Mn—Cr/90Co-10Fe(2.4)Cu(2.4)/Ta(4)films. The H_(UA) can reach as high as 650 Oe.

In addition, the Fe content of the Co—Fe film can be varied for an evenhigher H_(UA). FIG. 13 shows H_(CE) and H_(UA) versus the Ir—Mn—Cr filmthickness forAl—O(3)/Ni—Cr—Fe(3)/Ni—Fe(0.4)/Ir—Mn—Cr/77Co-23Fe(2.4)Cu(2.4)/Ta(4)films (thickness in nm). The H_(UA) can reach as high as 1,700 Oe.

Furthermore, the Cr content of the Ir—Mn—Cr longitudinal pinning layercan be varied to attain a designed H_(UA). FIG. 14 shows H_(CE) andH_(UA) versus the Cr content of the Ir—Mn—Cr film forAl—O(3)/Ni—Cr—Fe(3)/Ni—Fe(0.4)/Ir—Mn—Cr(15)/Ni—Fe(4)/Cu(2.4)/Ta(4) andAl—O(3)/Ni—Cr—Fe(3)/Ni—Fe(0.4)/Ir—Mn—Cr(15)/70Co-30Fe(2.4)/Cu(2.4)/Ta(4)films. The H_(UA) decreases with increasing the Cr content of theIr—Mn—Cr longitudinal pinning layer. The use of a Co—Fe film with the Fecontent ranging from 15 to 30 atomic percent has another advantage: theCo—Fe/Ni—Fe/Co—Fe sense layers may be simply replaced by a Co—Fe senselayer with an optimal Fe content and a nearly zero or negativesaturation magnetostriction. In summary, to ensure the viability of thisinvention, it is very crucial to select suitable films with optimalcompositions and thicknesses as the seed layers, the longitudinalpinning layers, and the sense layers.

While various embodiments have been described above, it should beunderstood that they have been presented by way of example only, and notlimitation. Other embodiments falling within the scope of this inventionmay also become apparent to those skilled in the art. Thus, the breadthand scope of this invention should not be limited by any of theabove-described exemplary embodiments, but should be defined only inaccordance with the following claims and their equivalents.

1. A bottom-type giant magnetoresistance (GMR) sensor overlaid with auniform longitudinal bias (LB) stack, the bottom-type GMR sensorcomprising: nonmagnetic and ferromagnetic seed layers; anantiferromagnetic transverse pinning layer; a ferromagnetic first pinnedlayer; a first nonmagnetic antiparallel-coupling spacer layer; aferromagnetic second pinned layer, the first nonmagneticantiparallel-coupling spacer layer being sandwiched between the firstand second pinned layers; a nonmagnetic conducting spacer layer; and aferromagnetic sense layer, the nonmagnetic conducting spacer layer beingsandwiched between the ferromagnetic second pinned layer and theferromagnetic sense layer; the uniform longitudinal bias (LB) stackcomprising: a second nonmagnetic antiparallel-coupling spacer layer; aferromagnetic longitudinal pinned layer, the second nonmagneticantiparallel-coupling spacer layer being sandwiched between the senselayer and the ferromagnetic longitudinal pinned layer; anantiferromagnetic longitudinal pinning layer in direct contact with andexchange-couple to the ferromagnetic longitudinal pinned layer; and anonmagnetic cap layer.
 2. A top-type GMR sensor overlying a uniformlongitudinal bias (LB) stack; the uniform longitudinal bias (LB) stackcomprising: nonmagnetic and ferromagnetic seed layers; anantiferromagnetic longitudinal pinning layer; the top-type GMR sensorcomprising: a ferromagnetic sense layer formed over and in directcontact with the longitudinal pinning layer; a nonmagnetic conductingspacer layer formed over the ferromagnetic sense layer; a ferromagneticfirst pinned layer formed over the nonmagnetic conducting spacer layer;a nonmagnetic antiparallel-coupling spacer layer formed over theferromagnetic first pinned layer; a ferromagnetic second pinned layerformed over the nonmagnetic antiparallel-coupling spacer layer; anantiferromagnetic transverse pinning layer formed over and exchangecoupled to the second ferromagnetic pinned layer; and a nonmagnetic caplayer.
 3. A top-type GMR sensor overlying a uniform longitudinal bias(LB) stack; the uniform longitudinal bias (LB) stack comprising:nonmagnetic and ferromagnetic seed layers; an antiferromagneticlongitudinal pinning layer; a ferromagnetic longitudinal pinned layer;and a first non-magnetic antiparallel-coupling spacer layer formed overthe ferromagnetic longitudinal pinned layer; the top-type GMR sensorcomprising: a ferromagnetic sense layer formed over and in directcontact with the first non-magnetic antiparallel-coupling spacer layer;a nonmagnetic conducting spacer layer formed over the ferromagneticsense layer; a ferromagnetic first pinned layer formed over thenonmagnetic conducting spacer layer; a second nonmagneticantiparallel-coupling spacer layer formed over the ferromagnetic firstpinned layer; a ferromagnetic second pinned layer formed over the secondnonmagnetic antiparallel-coupling spacer layer; an antiferromagnetictransverse pinning layer formed over and exchange coupled to the secondferromagnetic pinned layer; and a nonmagnetic cap layer formed over theantiferromagnetic transverse pinning layer.
 4. A GMR sensor as in claims2 wherein the ferromagnetic longitudinal pinned layer comprises either aferromagnetic Ni—Fe film with a thickness ranging from 10 to 30angstroms, or a ferromagnetic Co—Fe film with a thickness ranging from10 to 20 angstroms.
 5. A GMR sensor as in claims 4 wherein theferromagnetic longitudinal pinned layer comprises either a ferromagneticNi—Fe film with a thickness ranging from 10 to 30 angstroms, or aferromagnetic Co—Fe film with a thickness ranging from 10 to 20angstroms.
 6. A GMR sensor as in claim 2 wherein the nonmagneticantiparallel-coupling spacer layer used in the uniform LB stackcomprises a Ru film with a thickness preferably ranging from 4 to 10angstroms.
 7. A GMR sensor as in claim 4 wherein the nonmagneticantiparallel-coupling spacer layer used in the uniform LB stackcomprises a Ru film with a thickness preferably ranging from 4 to 10angstroms.
 8. A bottom-type tunneling magnetoresistance (TMR) sensoroverlaid with a uniform longitudinal bias (LB) stack; the bottom-typeTMR sensor comprising: nonmagnetic and ferromagnetic seed layer; anantiferromagnetic transverse pinning layer; a ferromagnetic first pinnedlayer; a first nonmagnetic antiparallel-coupling spacer layer; aferromagnetic second pinned layer; a nonmagnetic insulating barrierlayer; and a ferromagnetic sense layer; the uniform longitudinal bias(LB) stack comprising: a second nonmagnetic antiparallel-coupling spacerlayer; a ferromagnetic longitudinal pinned layer; an antiferromagneticlongitudinal pinning layer in direct contact with and exchange-couple tothe ferromagnetic longitudinal pinned layer; and a nonmagnetic caplayer.
 9. A top-type tunneling magnetoresistance (TMR) sensor overlyinga uniform longitudinal bias (LB) stack; the uniform longitudinal bias(LB) stack comprising: nonmagnetic and ferromagnetic seed layers; anantiferromagnetic longitudinal pinning layer; the top-type TMR sensorcomprising: a ferromagnetic sense layer in direct contact with thelongitudinal pinning layer; a nonmagnetic insulating barrier layer; aferromagnetic first pinned layer; a nonmagnetic antiparallel-couplingspacer layer; a ferromagnetic second pinned layer; an antiferromagnetictransverse pinning layer exchange coupled to the second ferromagneticpinned layer; and a nonmagnetic cap layer.
 10. A top-type tunnelingmagnetoresistance (TMR) sensor overlying a uniform longitudinal bias(LB) stack; the uniform longitudinal bias (LB) stack comprising:nonmagnetic and ferromagnetic seed layers; an antiferromagneticlongitudinal pinning layer; a ferromagnetic longitudinal pinned layer;and a first non-magnetic antiparallel-coupling layer; the top-type TMRsensor comprising: a ferromagnetic sense layer in direct contact withthe first non-magnetic antiparallel-coupling layer; a nonmagneticinsulating barrier layer; a ferromagnetic first pinned layer; a secondnonmagnetic antiparallel-coupling spacer layer; a ferromagnetic secondpinned layer; an antiferromagnetic transverse pinning layer exchangecoupled to the second ferromagnetic pinned layer; and a nonmagnetic caplayer.
 11. A TMR sensor as in claims 17, wherein the ferromagneticlongitudinal pinned layer comprises either a ferromagnetic Ni—Fe filmwith a thickness ranging from 10 to 30 angstroms, or a ferromagneticCo—Fe film with a thickness ranging from 10 to 20 angstroms.
 12. A TMRsensor as in claims 19, wherein the ferromagnetic longitudinal pinnedlayer comprises either a ferromagnetic Ni—Fe film with a thicknessranging from 10 to 30 angstroms, or a ferromagnetic Co—Fe film with athickness ranging from 10 to 20 angstroms.
 13. A TMR sensor as in claims17, wherein the nonmagnetic antiparallel-coupling spacer layer used inthe uniform LB stack comprises a Ru film with a thickness preferablyranging from 4 to 10 angstroms.
 14. A TMR sensor as in claims 19,wherein the nonmagnetic antiparallel-coupling spacer layer used in theuniform LB stack comprises a Ru film with a thickness preferably rangingfrom 4 to 10 angstroms.